The present invention relates to a method and apparatus for subjecting a target object, such as a semiconductor wafer or LCD substrate, to a process, using plasma generated by means of radio frequency (RF) discharge, and in particular to a method and apparatus for subjecting a target object having a large surface area to plasma etching or plasma deposition at a high planar uniformity and a high processing rate.
In processes of manufacturing semiconductors, various kinds of plasma processes, such as etching, are performed on a target object, such as a semiconductor wafer, in a plasma atmosphere, while plasma is generated in a process chamber. In recent years, target objects of this kind have become higher in their diameter or surface area, such that, for example, semiconductor wafers have changed their size from 6 inches to 8 inches and further to 12 inches (300 mm), in order to decrease the processing cost per unit surface area of the target objects.
In consideration of this demand, researches have been conducted on plasma processing apparatuses for processing a target object of a large surface area. It is thought that, as a type of generating plasma used in such processing apparatuses, the parallel plate type or the ICP (Inductively Coupled Plasma) type is promising. This is because, the other types of generating plasma, such as the ECR (Electron Cyclotron Resonance) type and the helicon wave type, are apt to produce a plurality of modes, thereby bringing about a difficulty in obtaining uniform plasma, when a plasma source becomes large in accordance with a target object.
There is another problem caused due to a large magnet in these plasma processing apparatuses. In this case, where plasma is spread by means of diffusion due to gradient of a magnetic field without making a plasma source larger, electrons are accelerated at the peripheral region, thereby causing plasma properties to be different between the central region and the peripheral region.
Further, if a wafer larger than an 8-inch (200 mm) wafer needs to be provided with process properties, such as processing rate, selectivity, and processed shape, which are equal to those obtained relative to the 8-inch wafer, the flow rate of a process gas should be increased in proportion to an increase in the surface area of the target surface. In this case, where the height of a plasma space, i.e., the distance between upper and lower electrodes in the parallel plate type, is maintained to be equal to that of a conventional apparatus, the aspect ratio of the plasma space between its height and width becomes greater with an increase in the surface area of the target surface, thereby reducing its exhausting conductance. As a result, a high vacuum suitable for a plasma process is hardly obtained while causing a large predetermined amount of a processing gas to flow, in consideration of the performance of, e.g., a vacuum pump currently being used. For example, as compared with an 8-inch wafer, a 300-mm (12-inch) wafer increases its surface area 2.24 times larger, and thus requires a 2.24 times greater amount of processing gas, thereby bringing about a difficulty in vacuum exhaustion. Further, exhaustion of a reactive gas differs between the central and peripheral regions of the target surface, and thus process properties, such as a processing rate, are not uniform between the central and peripheral regions of the target surface.
It can be assumed that the exhausting conductance should be increased by expanding the distance between the electrodes so as to allow the vacuum exhaustion to be performed easily. In this case, however, if its dissociated gas state is to be the same as that in a conventional apparatus while preventing the plasma density from lowering, it is necessary to set the residence time of the gas in the plasma space to be also equal. As a result, the flowing amount of the gas has to be increased, thereby further bringing about a difficulty in vacuum exhaustion.